As electric/electronic products become smaller, more highly integrated, and lighter, interior parts thereof need to be fabricated into a module. For example, an interior frame requiring ground-connection capability should have electrical conductivity and high mechanical strength, while an exterior material requiring EMI/RFI shielding properties should provide EMI/RFI shielding and have a desirable appearance.
Conventionally, these functions have been realized by combining materials having each characteristic. There is an increasing need, however, for a multi-functional material having high strength, electromagnetic wave shielding characteristic, and the like to satisfy the requirements for down-sized, highly integrated, and lighter electric/electronic products.
A conventional method of shielding electromagnetic waves includes coating/plating a metal material. The metal material has high conductivity (R, low impedance) and thus, a high electromagnetic wave shielding ratio by reflecting an electromagnetic wave on the surface. Accordingly, even a thin metal coating may effectively shield an electromagnetic wave. However, the coating/plating is a complex process and may deteriorate productivity.
U.S. Patent Publication No. 2007-0199738 discloses a electromagnetic wave shielding device including a polymer substrate coated with metal on its surface. U.S. Patent Publication No. 2007-0056769 discloses an electromagnetic wave shield material including a non-conductive polymer, a conductive polymer, and an electrical conductive metal powder. U.S. Publication No. 2002-0108699 discloses a method of manufacturing an electrically conductive impregnated fiber by coating a conductive fiber with a compatibilizer such as an organic wetting agent, and compositing the same in a resin. U.S. Pat. No. 6,638,448 discloses an electrically conductive thermoplastic elastomer including a conductive filler of nickel plated with silver in a styrene-ethylene-butadiene-styrene copolymer (SEBS) based matrix material which is a non-conductive resin. U.S. Pat. No. 6,409,942 discloses an electrically conductive composition in which a carbonaceous conductive filler is immersed in a blend of two polymer resins having different polarities and the carbonaceous conductive filler is disposed on one having the higher polarity. U.S. Pat. No. 5,869,412 discloses a thermoplastic electromagnetic wave shielding sheet including a sheet material or polymer carrier that is capable of forming pores during a thermoplastic process and including a low-melting point metal conductive filler. However, these technologies may not provide all of the various properties increasingly required for electric and electronic products, such as high strength, high electrical conductivity, and EMI/RFI shielding properties.